In spite of the progress made in the ECC field since it appeared early 1950s, it still presents drawbacks that give rise to postoperative hemodynamic disorders.
The artificial surfaces of the ECC activate coagulation and platelets, giving rise to a very high probability of clots forming inside the circuit, which can lead to difficult situations such as postoperative bleeding, and biochemical and electrolytic disorders.
The laminar flow in conventional ECC deprives the endothelium of the stimuli of tangential shear stress forces, leading to an endothelial malfunction syndrome that is responsible for activating the complement cascade, the inflammatory response, apoptosis, and hemodynamic disorders, in particular with newborns and children.
The circulation of a fluid in a closed hydraulic circuit (energy transfer with loss of head by friction) depends on the source of energy, the shape of the tubes, and the viscosity and the density of the fluid.
The three main physical laws involved in this mechanism are the following: Newton's law concerning shear force (1668); Bernoulli's third equation concerning energy losses (1738); and Reynolds numbers (1880) that define the density and the movement profile of the liquid.
ECC is based on theories relying on Newtonian fluids at constant viscosity traveling in a closed circuit with unchanging tube geometry.
Cardiovascular circulation contains a non-Newtonian fluid, which moves in vessels that are of variable geometry.
There is thus a confrontation between two different kinds of hydraulic circuit and there are difficulties in adapting them functionally to each other and making them work together harmoniously.
Vascular resistances to cardiovascular circulation are controlled mainly by secreting nitrogen monoxide (NO), and that depends on the endothelial stimulation by shear force. In contrast, in ECC, resistances are more linked to the type of tube, to the oxygenator, to the aortic cannula, to the viscosity, and to the flow being laminar or turbulent.
In practice, this means that it is necessary to quantify the circulatory driving force, whether it be natural (the heart) or artificial (ECC). This circulatory driving force depends on its capacity to move blood with low resistances and thus to maintain vascular tonus and endothelial functions by shear stress, using a regular pulsatile flow including pulse pressure that is physiological.
In order to overcome those drawbacks of conventional ECC, various theoretical strategies have been applied:                the use of medications such as anticoagulants, inotropics, vasodilatators, hormones, electrolytes, blood, platelets, or other substitutes, and this has not completely solved hemodynamic problems while giving rise to specific undesirable effects;        ECC at normal temperature: this is becoming more and more widespread, replacing low temperature ECC. Normal temperature makes blood practically Newtonian, thereby limiting head losses and the inflammatory response, particularly inside the ECC circuit. Nevertheless, its action on the heart and blood vessels is always open to question since the myocardium is protected by cardioplegia injections and microcirculation is facilitated by hemodilution (Fahraeus-Lindqvist) effect;        beating heart surgery without ECC. Beside the beneficial effects on postoperative hemodynamics, such a technique is difficult, and can only be used on patients with few complex needs. It requires specific equipment for holding still the portion on which the operation is being performed, thus making the method expensive;        pulsatile ECC: in order to conserve shear stress stimulation and conserve the endothelial function during surgery, a pulsatile mode of perfusion has been used by various groups over the last three decades. At present, new generations of pulsatile ECC equipment makes use of peristaltic or centrifugal pumps modified for generating a pulsatile perfusion flow. That usually requires two arterial pump heads, one upstream and one downstream from the oxygenator, in order to limit its obstructive effect. That therefore requires special high-technology equipment of high cost, and with mediocre induced pressure curves. Such equipment is therefore not very widespread.        
It may be observed that practically all pulsatile machines have been evaluated using Bernoulli's energy loss equations and the perfusion of microcirculation during ECC depends on the hemodilution more than on the type of driving force used. Similarly, it appears paradoxical to apply pulses to a fluid such as blood with its very fragile components in a long rigid tube of small diameter, regardless of the material from which it is made, e.g. polyvinylchloride (PVC) or silicone, and with its undesirable effects of microembolisms.
Another method for obtaining a certain amount of pulsation during conventional ECC (with a continuous flow) is to add an intra-aortic counter-pulsation balloon that is inserted invasively into the thoracic aorta. Although inexpensive and correlated with pulsatile ECC, that method remains invasive, with vascular complications, especially with children or adults suffering from atherosclerosis.
In conclusion, those methods are usually evaluated by the improved perfusion of localized organs such as the renal or splanchnic areas, but provide little protection to distal organs such as cerebral circulation. That creates zones of turbulent shear or Reynolds stress with vortexes close to the walls of blood vessels, vortexes created by two opposing flows meeting, i.e. the laminar ECC flow and the pulsatile flow from the balloon, thereby compromising regional endothelium.
The methods mentioned above thus do not solve the undesirable effects of ECC.
The inventors have proposed a solution in international application WO 2008/000110. That solution consists in a pulsatile tube having a so-called “two-lumen” portion in which the inflatable tube is incorporated in an intra-lumen or extra-lumen manner.
The present invention consists in an improvement of that two-lumen pulsatile tube.